package com.note.simpleadmin.utils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class IdWorker {  
      
    protected static final Logger LOG = LoggerFactory.getLogger(IdWorker.class);  
      
    private long workerId;  
    private long datacenterId;  
    private long sequence = 0L;  
  
    private long twepoch = 1288834974657L;  
  
    private long workerIdBits = 5L;  
    private long datacenterIdBits = 5L;  
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);  
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);  
    private long sequenceBits = 12L;  
  
    private long workerIdShift = sequenceBits;  
    private long datacenterIdShift = sequenceBits + workerIdBits;  
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;  
    private long sequenceMask = -1L ^ (-1L << sequenceBits);  
  
    private long lastTimestamp = -1L;  
  
    public IdWorker(long workerId, long datacenterId) {  
        // sanity check for workerId  
        if (workerId > maxWorkerId || workerId < 0) {  
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));  
        }  
        if (datacenterId > maxDatacenterId || datacenterId < 0) {  
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));  
        }  
        this.workerId = workerId;  
        this.datacenterId = datacenterId;  
        LOG.info(String.format("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d", timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId));  
    }  
  
    public synchronized long nextId() {  
        long timestamp = timeGen();  
  
        if (timestamp < lastTimestamp) {  
            LOG.error(String.format("clock is moving backwards.  Rejecting requests until %d.", lastTimestamp));  
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));  
        }  
  
        if (lastTimestamp == timestamp) {  
            sequence = (sequence + 1) & sequenceMask;  
            if (sequence == 0) {  
                timestamp = tilNextMillis(lastTimestamp);  
            }  
        } else {  
            sequence = 0L;  
        }  
  
        lastTimestamp = timestamp;  
  
        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;  
    }  
  
    protected long tilNextMillis(long lastTimestamp) {  
        long timestamp = timeGen();  
        while (timestamp <= lastTimestamp) {  
            timestamp = timeGen();  
        }  
        return timestamp;  
    }  
  
    protected long timeGen() {  
        return System.currentTimeMillis();  
    }  
}  